Question

What are the two main measures of diversity? Do you understand how to plot a species accumulation curve and how to interpret it? What about rank abundance curves/graphs?

Answer 1

Two important factors that are considered for measuring diversity are richness and evenness. Richness is a measure of the number of different kinds of organisms present in a particular area. The number of species per sample is a measure of richness. More the species present in a sample, richer the sample. Evenness compares the similarity of the population size of each of the species present. In other words, evenness is a measure of the relative abundance of the different species making up the richness of an area.

Species accumulation curve

Species accumulation curves show the rate at which new species are found within a niche and can be extrapolated to provide an estimate of species richness in terms of diversity. The collectors curve is the simplest of the type of species accumulation curve. This plots the cumulative number of species recorded as a function of sampling effort (i.e. number of individuals collected or cumulative number of samples). The order in which samples are included in a species accumulation curve will influence the overall shape. A smooth accumulation curve can be produced by repeating a process of randomly adding the samples to the accumulation curve and then plotting the mean of these permutations. Example curve is shown as below:

Rank abundance curve

A rank abundance curve is also called as Whittaker plot. It is a chart that display relative species abundance in terms of diversity. It can also be used to visualize species richness and species evenness. It overcomes the shortcomings of biodiversity indices that cannot display the relative role different variables played in their calculation. A rank abundance curve is a chart with relative abundance on the Y-axis (this is a measure of a species abundance (e.g., the number of individuals) relative to the abundance of other species) and the abundance rank on the X-axis (The most abundant species is given rank 1, the second most abundant is 2 and so on). Example curve is as shown below: